1. Field of the Invention
The present invention pertains to wireless telecommunications, and particularly to release of radio connections in a radio access network.
2. Related Art and Other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The term “user equipment unit (UE)” herein is used synonymously with mobile terminal and mobile station. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cells, with each cell being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core network nodes.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs).
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “lub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface” or “Uu interface”. In some instances, a connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC. An Inter-RNC transport link can be utilized for the transport of control and data signals between Source RNC and a Drift or Target RNC, and can be either a direct link or a logical link as described, for example, in International Application Number PCT/US94/12419 (International Publication Number WO 95/15665). An interface between radio network controllers (e.g., between a Serving RNC [SRNC] and a Drift RNC [DRNC]) is termed the “lur” interface.
The radio network controller (RNC) controls the UTRAN. In fulfilling its control role, the RNC manages resources of the UTRAN. Such resources managed by the RNC include (among others) the downlink (DL) power transmitted by the base stations; the uplink (UL) interference perceived by the base stations; and the hardware situated at the base stations.
Those skilled in the art appreciate that, with respect to a certain RAN-UE connection, an RNC can either have the role of a serving RNC (SRNC) or the role of a drift RNC (DRNC). If an RNC is a serving RNC (SRNC), the RNC is in charge of the connection with the user equipment unit (UE), e.g., it has full control of the connection within the radio access network (RAN). A serving RNC (SRNC) is connected to the core network. On the other hand, if an RNC is a drift RNC (DRNC), its supports the serving RNC (SRNC) by supplying radio resources (within the cells controlled by the drift RNC (DRNC)) needed for a connection with the user equipment unit (UE). A system which includes the drift radio network controller (DRNC) and the base stations controlled over the lub Interface by the drift radio network controller (DRNC) is herein referenced as a DRNC subsystem or DRNS.
Operation of a user equipment unit (UE) is conceptualized as having two modes: an Idle Mode and a Connection Mode. The Idle Mode is entered after power on. In Idle Mode there is no connection between the user equipment unit (UE) and the UTRAN. When a connection is established, the user equipment unit (UE) is assigned a U-RNTI and the user equipment unit (UE) enters Connected Mode. The U-RNTI (UTRAN Radio Network Temporary Identity) is a global identity, which can be used in any cell in the UTRAN.
Within Connected Mode there are four different states: CELL_DCH state; CELL_FACH state; CELL_PCH state; and URA_PCH . Each state reflects a different level of activity.
A release of a radio connection between the radio access network (like UTRAN) and the mobile terminal (like the user equipment unit (UE)) involves the mobile terminal leaving the connected mode and entering the idle mode. In current cellular systems, there are several methods for releasing the connection. In the normal case, the network or user equipment unit (UE) sends a RELEASE message to the other party on the dedicated control channel (DCCH). The other party acknowledges, either indirectly by releasing the channel which can be detected or by transmitting a RELEASE COMPLETE or similar acknowledgement message, and enters the idle mode, and the initiating party can enter idle mode as well. After the release, the U-RNTI that was allocated by the now-released connection can be reused by another connection.
A possibility has been introduced in WCDMA to transmit the RELEASE message on a common control channel (CCCH). The purpose of this solution is to enable the DRNC to release the connection to a given user equipment unit (UE), if the SRNC can not transmit the message (the DCCH originates in the SRNC).
In a failure case, when the radio connection is lost, the user equipment unit (UE) and UTRAN enter Idle Mode when a failure is detected. Failure detection is quickest in the CELL_DCH state, as the physical channel is lost in that case. In the CELL_FACH, CELL_PCH and URA_PCH states, failure detection is much slower since it relies on a periodic supervision mechanism every set number of minutes, where the user equipment unit (UE) makes periodic CELL UPDATE or URA UPDATE depending on the state.
In the conventional practice, only one user equipment unit (UE) at a time can be released using the RELEASE message sent from UTRAN to the user equipment unit (UE). Radio connection release on a UE by UE basis is satisfactory in most situations. However, in a failure situation when all connections belonging to an RNC (SRNC or DRNC) have to be released (like restart of RNC or a reset is received from the core network), this conventional practice entails an enormous amount of signaling messages. Such massive signaling causes significant load in the radio network control (RNC) node(s) as well over the radio interface. Since the resources are limited, the RELEASE messages can not be sent instantaneously to all UEs and thus they will take some time to transmit. This delay will typically cause inconvenience for the user. Moreover, this delay increases a risk that a U-RNTI, already in use by a first user equipment unit (UE), will be prematurely allocated to a new connection. Furthermore, in case of restart of an radio network control (RNC) node, the RNC may forget which U-RNTIs were allocated to user equipment units (UEs) before the restart.
What is needed, therefore, and an object of the present invention, is a technique for providing more efficient release of radio connections in a radio access network.